1. Field of the Invention
The present invention relates generally to press working techniques and, more specifically, to a work following device and method for automatically following a work being pressed on a press such as a press brake.
2. Description of the Prior Art
In pressing a work, for example, a thin plate, on a press such as a press brake, the work needs to be positioned on the press accurately and the work needs to be held properly during the press working so that the work will not be deformed.
FIG. 18 illustrates a conventional press brake 1 in operation. The bending press 1 has a ram 2 which is lowered for press working, and a bed 5 provided with dovetail grooves 11. A movable bending die 3 is secured to the ram 2 with bolts 4, and a fixed bending die 6 is fixed in place on the bed 5 by means of holding bars 7, fulcrums 8, bolts 9 and nuts 10 using the dovetail grooves 11 of the bed 5.
In press working, a work 13 such as a flat plate is positioned accurately relative to the fixed bending die 6, and then a foot switch 14 is pressed to lower the ram 2, so that the work 13 is bent in a predetermined size between the movable bending die 3 and the fixed bending die 6. Then, the foot switch 14 is pressed again to raise the ram 2 to separate the movable bending die 3 from the fixed bending die 6. Then, the pressed work 13 is transferred from the bending press 1 to a delivery table, not shown. This press working cycle is repeated to bend works successively.
Problem occurs in bending the work 13 when the same is a comparatively large thin plate. Referring to FIG. 19, when such a comparatively large work 13 is pressed on the bending press 1 to bend one longitudinal side portion of the work 13, the opposite longitudinal side portion 13a of the same moves as indicated by an arrow as the work 13 is bent between the movable bending die 3 and the fixed bending die 6, in which the longitudinal side portion 13a is liable to move excessively by inertia to a position C beyond a normal position B and stops with a residual warp. To suppress such an undesirable movement of the longitudinal side portion 13a, the operator 12 is required to hold the longitudinal side portion 13a by hand to follow the movement of the longitudinal side portion 13a during the press working as illustrated in FIG. 18. Such a work is very dangerous to the operator 12.
To facilitate a press working and to eliminate such a dangerous manual work, in advanced press mills, an industrial robot for feeding a work to and removing a pressed work from a bending press, and a numerically controlled hydraulic work following apparatus which holds the work following the movement of the work during press working are employed in combination with a bending press. The work following apparatus positions a work fed by the industrial robot to the bending press accurately for press working, prevents the undesirable deformation of the work during press working and positions the pressed work accurately for removal by the industrial robot. However, the known work following apparatus requires a large floor space for installation in addition to a floor space for installing the bending press and has a complicated construction, which is disadvantageous in practical application of the work following apparatus.